When Samantha Amato needed a nanny to look after her 8-month-old twins, she hired a nanny placement agency, which recommended several candidates after checking their criminal and employment backgrounds. Amato was not satisfied. She called one candidate’s references herself. She interviewed the woman’s former co-workers at a nearby day care, as well as mothers who had known her work at the center.

In the end, she hired the woman — a mother in her 40s with whom she found an enduring comfort level. She still feels confident about her choice, but Tuesday’s news of a nanny charged with assaulting a Cambridge girl who subsequently died brings back the uncertainty she felt at the prospect of leaving her child in the care of a stranger.

“It’s terrifying. You’re leaving your life in the hands of someone you don’t know ­essentially,” said Amato, a business manager at a book distribution company who lives in North Easton.

For Boston-area parents, finding a trustworthy in-home caretaker for children is fraught with the memory of the death of a baby in the care of British au pair Louise Woodward in 1997, and now allegations that Irish national Aisling McCarthy Brady ­assaulted the 1-year-old girl.

Unlike day-care providers, who are licensed by the state Department of Early Education and Care, nannies are not licensed, meaning that they are hired at the discretion of parents.

Jennifer Russo, a placement counselor for Boston Nanny Centre Inc. in Newton, said her agency conducts extensive checks on nanny candidates — including local criminal records searches and working with a private investigator to do more extensive ­national reviews.

The agency also requires five to six references from each candidate, three of which must come from professional child-care employers. The confidential conversations with references are often crucial, Russo said.

“Sometimes when we have called, the families have told us that they told the woman they had to cut her hours, when ­really they had sensed she was too rigid or had shown a temper,” Russo said.

Russo said her agency rejects more than 80 percent of its applicants.

“We don’t even bother to continue the screening process with someone we have an iffy feeling about,” she said.

Susan Tokayer, co-president of the International ­Nanny Association, said the ­Internet has meant that more people bypass nanny agencies, instead choosing a nanny from Craigslist or online services. She said the online services’ background checks can be insufficient.

“It puts the onus back on the family to do the background checks,” she said.

She said the Internet opens up the possibility for a family to do a search themselves — but not everyone knows what to check.

Her agency recommends that a background check include: employment and identity verification, state and county criminal record searches for every jurisdiction where the candidate has worked and lived for at least the past seven years, a sex offender registry search in all 50 states, and a review of the candidate’s driving record.

Bob Sheehan, the owner of Sheehan Security Services in Londonderry, N.H., which runs checks for Boston Nanny Centre, said he has conducted thousands of checks on nanny candidates since 1994, rarely turning up criminal histories. But there are notable exceptions, and some of his searches have found records of bank robbery, assault with a deadly weapon, drug charges, and shoplifting.

“We’ve even had cases where people weren’t who they said they were, sending someone else to the interview,” he said.

According to FBI statistics analyzed by James Alan Fox, a criminologist at Northeastern University, the number of reported killings of children younger than a year old by a baby sitter hasn’t changed significantly since 1976, when there were 20.

In 2010, 18 were killed by a baby sitter.

Deborah Eappen said the death of her son, Matthew, in 1997 in the care of Louise Woodward remains a source of ongoing pain for her family.

“The impact of losing a child to abuse and violence — the impact is something that ripples through all our lives. It continues to ripple. It’s really the ultimate betrayal of trust,” she said.

Her family operates the Matty Eappen Foundation, which seeks to prevent abusive head trauma through public awareness and education and assists victims.

News of the abuse of the Cambridge child allegedly at the hands of a nanny underscored the difficulty for parents in hiring a caretaker for children, she said.

“There have been huge changes in the child-care world, nanny-cams, for one,” said Eappen, a doctor. “But the truth of the matter is most ­people try to be very careful in who they select to care for their children, but even with the best people, you cannot predict behavior.”